1. Field of the Invention
This invention relates to a reusable fixture for a carrier tape for holding a carrier tape of the TCP (Tape Carrier Package) type.
2. Description of the Related Art
In recent years, as high density mounting of IC (Integrated Circuit) and LSI (Large Scale Integration) packages onto circuit boards proceeds, the reduction in size and pitch and the increase in the number of pins of packages have been and are proceeding rapidly.
Therefore, attention is paid to TCPs of the TAB (Tape Automated Bonding) type with which reduction in size and reduction in pitch of packages can be anticipated sufficiently. The TCPs of the TAB type have the general structure of a small, thin IC package wherein IC chips are incorporated in a carrier tape and molded with a resin by transfer molding.
As the reduction in pitch and the increase in the number of pins proceed, it becomes difficult to keep fine lead terminals accurate until immediately before the package is mounted onto a circuit board. Therefore, it is a conventional practice to provide a reusable fixture as a guard ring and cut and form the carrier tape immediately before mounting the package onto a circuit board. The general structure of a reusable fixture for a carrier tape comprises a bottom element having a square hole formed at a central portion thereof for allowing bonding of an IC chip, a frame formed so as to surround the outer periphery of the bottom member in order to protect the carrier tape, and a tape holding member for holding the carrier tape to the bottom member in the frame. A conventional reusable fixture will be described below.
FIG. 1 is a schematic plan view of an example of a conventional reusable fixture disclosed in U.S. Pat. No. 4,069,496 and shows a condition wherein a carrier tape is fitted in the reusable fixture. FIG. 2 is a sectional view taken along line A--A of FIG. 1 showing the reusable fixture of FIG. 1.
As shown in FIGS. 1 and 2, the reusable fixture includes a reusable fixture body 54 on which a plurality of hook-shaped tape holding members 55 corresponding to sprocket holes 53 in a carrier tape 52 are provided integrally. The carrier tape 52 is connected to an IC chip 51 and held on the reusable fixture body 54 with the sprocket holes 53 thereof engaged with the tape holding members 55.
Another reusable fixture having a different structure for holding a carrier tape 52 is also known and shown in FIGS. 3 and 4.
FIG. 3 is a schematic plan view of another example of a conventional reusable fixture disclosed in U.S. Pat. No. 4,937,655 and shows a condition in which a carrier tape is fitted in the reusable fixture. FIG. 4 is an enlarged schematic view of a tape holding member of the reusable fixture shown in FIG. 3 and illustrates the relationship between the tape holding member and a jig. As shown in FIGS. 3 and 4, reusable fixture body 63 has resilient tape holding members 66 provided integrally at the four corners thereof. Meanwhile, an automated machine for mounting the carrier tape 62 onto the reusable fixture body 63 includes a jig 68 in the form of pins provided as engaging members for the tape holding members 66, the pins being movable in an opposing relationship to each other on straight lines toward the outer sides of the reusable fixture body 63. In the reusable fixture, the jig members 68 are first engaged with the respective tape holding members 66, and the tape holding members 66 are then simultaneously pulled to the outer sides (in the leftward and rightward directions in FIG. 3) and the tape positioning pins 64 of the reusable fixture body 63 are inserted into sprocket holes 65 of the carrier tape 62. Consequently, the carrier tape 62 is disposed at a predetermined position. When the jig members 68 are returned to their original positions, the tape holding members 66 restore the respective original positions due to their resiliency so that they extend above the four corners of the carrier tape 62, thereby holding the carrier tape 62 on the reusable fixture body 63.
However, with the reusable fixture of the prior art described above and shown in FIGS. 1 and 2, when the heads of the tape holding members 55 are passed through the sprocket holes 53 of the carrier tape 52, the sprocket holes 53 are expanded so forcibly by the tape holding members 55 that portions of carrier tape 52 around sprocket holes 53 may be deformed in such a manner as to cause the carrier tape 52 to bend up. In some cases, the carrier tape 52 may be cracked or broken.
If such deformation or damage actually occurs, the sprocket holes 53 of the carrier tape 52 may possibly be disengaged during transportation of the reusable fixture 54 on which the carrier tape 52 is mounted and the tape holding members 55 may release the carrier tape 52 from the reusable fixture body 54. Consequently, there is a problem in that the holding of the carrier tape 52 on the reusable fixture body 54 may become unstable.
With the reusable fixture shown in FIGS. 3 and 4, when the jig members 68 push simultaneously at the four locations to expand to the outer sides (in the leftward and rightward directions in FIG. 3) the tape holding members 66 which are movable in an opposing relationship to each other on the straight lines, since each of the tape holding members 66 is supported in a cantilever structure on the reusable fixture body 63, each tape holding member 66 is deformed around a fulcrum at the joining portion 67 thereof to the reusable fixture body 63, and thereupon, an arbitrary point of the tape holding member 66 will move in an arc.
As shown in FIG. 4, each jig member 68 moves in contact with the tape holding member 66a on a straight line in the direction of jig member movement 71 from the first contact point 69 at which it contacts the tape holding member 66abefore the tape holding member 66a is deformed to a second contact point 70 at which it is in contact with the tape holding member 66 after the tape holding member 66a is deformed fully. Upon the movement of the jig member, the tape holding member 66 and the jig member 68 slidably move relative to each other, thereby producing powder as a result of friction. If the friction powder sticks between electrode terminals of a narrow pitch or to a bonding surface, an IC chip mounted on the reusable fixture may possibly be short-circuited.
The present invention has been made in view of the problems of the prior art described above, and it is an object of the present invention to provide a reusable fixture which allows a carrier tape to be mounted thereon using an apparatus of a simple structure and which does not produce powder from friction when the carrier tape is mounted and which in addition can hold the carrier tape precisely and securely.